Fix NPE in when dropping from all apps (issue 12917451)

When dropping from all apps, accept drop was returning true if the item
was above a folder, however, when it came time to complete the drop,
the folder wouldn't accept the item. This can be prevented by increasing
the criteria in acceptDrop.

Change-Id: Ib644ec45984e8366c33bb674f3d3a76e22ed5160